GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR ENHANCES 5-LIPOXYGENASE LEVELS IN HUMAN POLYMORPHONUCLEAR LEUKOCYTES

Stimulation of human polymorphonuclear leukocytes (PMNL) with granuloc yte-macrophage CSF (GM-CSF) results in the enhanced expression of seve ral genes, including some coding for cytokines and enzymes. In this st udy, we investigated the ability of GM-CSF to up-regulate the human ne utrophil 5-lipoxygenase (5-LO), a key enzyme in the leukotriene synthe tic pathway. GM-CSF induced a dose- and time-dependent de novo synthes is of the 5-LO in PMNL, as determined by immunoprecipitation of S-35-m ethionine-labeled 5-LO. This up-regulation occurred within 30 min of t reatment with GM-CSF and was observed using concentrations of GM-CSF a s low as 30 pM. Prior treatment of the cells with the protein synthesi s inhibitor cycloheximide abolished this effect of GM-CSF. Western blo t analyses demonstrated that levels of 5-LO did not vary over a 6-h pe riod in unstimulated PMNL treated with CX, and that GM-CSF induced a r apid increase in the total cellular level of 5-LO protein; taken toget her these results indicated a translational effect of GM-CSF on the ex pression of the 5-LO. However, GM-CSF did not significantly affect the level of 5-LO mRNA in neutrophils, as determined by Northern blot ana lysis. Furthermore GM-CSF did not alter the stability of 5-LO mRNA, in agreement with a posttranscriptional effect of GM-CSF on 5-LO express ion in PMNL. These results show that human PMNL are capable of up-regu lating the expression of the 5-LO in response to physiologic activatio n.